1. Field of the Invention
The present invention relates to magnetic detectors for detecting leakage magnetic fields by measuring the change in electrical resistance. The present invention particularly relates to a magnetic detector which includes bias layers with a large coercive force, which has low junction resistance, and which therefore has high output and also relates to a method for manufacturing such a magnetic detector.
2. Description of the Related Art
Japanese Unexamined Patent Application Publication No. 2002-232037 (hereinafter referred to as Patent Document 1) discloses a method for manufacturing a magnetic detector as shown in FIGS. 5 to 10 of Patent Document 1. FIGS. 9 to 13 used herein correspond to FIGS. 5 to 10 of Patent Document 1 and show steps of manufacturing the magnetic detector in such a manner that a face of the magnetic detector is viewed from a recording medium.
In the method disclosed in Patent Document 1, as shown in FIG. 9, the following layers are formed on a lower gap layer 121 in this order: a seed layer 122, an antiferromagnetic layer 123, a first magnetic sub-layer 124a, a non-magnetic intermediate sub-layer 124c, a second magnetic sub-layer 124b, a non-magnetic intermediate layer 125, a free magnetic layer 126, a protective layer 127, and a resist layer 160. The first magnetic sub-layer 124a, the non-magnetic intermediate sub-layer 124c, and the second magnetic sub-layer 124b form a pinned magnetic layer 124. The antiferromagnetic layer 123, the pinned magnetic layer 124, the non-magnetic intermediate layer 125, the free magnetic layer 126, and the protective layer 127 form a multilayer film 131.
As shown in FIG. 10, both side regions of the multilayer film 131 are partly etched off, whereby recessed sections 131a are formed. In this step, the multilayer film 131 is etched such that the recessed sections 131a extend from the protective layer 127 into the antiferromagnetic layer 123.
As shown in FIG. 11, amorphous barrier layers 140 are formed in the recessed sections 131a so as to lie on the antiferromagnetic layer 123. Bias base layers 141 are formed over the amorphous barrier layers 140 and the inside walls 131b of the recessed sections 131a. As shown in FIG. 12, hard bias layers 142 are formed on the bias base layers 141. As shown in FIG. 13, electrode layers 143 and protective layers 144 are formed on the hard bias layers 142 in that order and the resist layer 160 is then removed, whereby the magnetic detector, which is represented by reference numeral 101, is obtained as shown in FIG. 14.
In the magnetic detector 101, since the amorphous barrier layers 140, the bias base layers 141, and the hard bias layers 142 are arranged on the antiferromagnetic layer 123 placed in the recessed sections 131a in that order, the bias base layers 141 are not in contact with the antiferromagnetic layer 123. That is, the amorphous barrier layers 140 having no definite crystalline structure are placed between the antiferromagnetic layer 123 and the bias base layers 141. Therefore, the crystal orientation of the bias base layers 141 is independent from the crystal orientation of the antiferromagnetic layer 123. This leads to an increase in the coercive force (Hc) of the hard bias layers 142 placed on the hard bias layers 142.
In the steps, shown in FIGS. 9 to 13, for manufacturing the magnetic detector 101, the step of etching both side regions of the multilayer film 131 to form the recessed sections 131a as shown in FIG. 10 is assumed to be performed in a vacuum. Furthermore, the step of forming the amorphous barrier layers 140 in the recessed sections 131a as shown in FIG. 11 is also assumed to be performed in a vacuum,as usual.
Although it is not disclosed in Patent Document 1 whether the step of forming the recessed sections 131a as shown in FIG. 10 and the step of forming the amorphous barrier layers 140 as shown in FIG. 11 are sequentially performed in the same vacuum, there is the following description in Paragraph [0148] of Patent Document 1: “etching is performed by ion milling, whereby a substrate including an antiferromagnetic layer with a thickness of 150 Å is prepared; and an amorphous barrier layer with a thickness of 25 Å is then formed on the substrate, whereby each sample is prepared”. That is, it is literally clear that the etching step and the amorphous barrier layer-forming step are separately performed. Hence, in the method disclosed in Patent Document 1, the step of etching both side regions of the multilayer film 131 to form the recessed sections 131a and the step of forming the amorphous barrier layers 140 in the recessed sections 131a are assumed not to be sequentially performed in the same vacuum.
The inventors have found that when the recessed sections 131a and the amorphous barrier layers 140 are non-sequentially formed in different vacuums, the hard bias layers 142 cannot have a large coercive force (Hc) unless the amorphous barrier layers 140 have a large thickness.
When the amorphous barrier layers 140 have a larger thickness, the amorphous barrier layers 140 have a larger portions in contact with the inside walls 131b. Therefore, when currents are applied between the electrode layers 143, currents flow in the portions of the amorphous barrier layers 140 that are in contact with the inside walls 131b. That is, an increase in the area of the portions of the amorphous barrier layers 140 that are in contact with the inside walls 131b causes a problem of an increase in junction resistance.